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Old 9th April 2011, 11:36 PM   #1
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Default 3rd order sealed series cap?

Hi guys no too up on this, has anyone tried it? I cannot find much info on this at all.
I have two ACI SV12 on the bottom (60lt sealed heavy stuffed) of my Martin Logan ESL Monoliths active 24db crossed over at 150hz, they sound very very good compared to the rubbish Eminence drivers ML put in there originally.
I've since been made aware of this (attached) that ACI put out which is a series 2500uf cap with the driver that flattens out and extends the response. I know that it lowers the effiecency by around 2db, but it takes out the slight hump and goes down further.
Is there any disadavtage like damping control over the cone?
I have ordered 4 X Nippon Chemi-con 4700uf caps that back to back will give me 2350uf, but these are standard caps and I believe that very low esr ones should be use, but I cannot find any cheap enough for this experiment.
Any thoughts on this by anyone?

Also I believe that B&W used this on their 801's and Infinity on their IRS and more expensive range, both these manufacturers always seamed to get great bass from their designs?
It also can also can protect the driver from an amp that goes DC

Cheers George
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Last edited by georgehifi; 9th April 2011 at 11:59 PM.
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Old 10th April 2011, 03:21 AM   #2
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The principle is sound.

The idea is you have a high Qtc (above 1.4 or so) sealed alignment. This will have a big impedance peak at Fb. The left side of the peak is largely inductive, the right side is capacitive.

The capacitor is tuned to the left side a bit below the peak. This causes the impedance at the resonant frequency to drop to 0Ω plus the DC resistance of the voice-coil. It makes the coil draw more power at its resonant frequency, thus playing louder.

I think it best implemented with high ripple current polarized power supply type capacitors, with small audio grade types in parallel to trim to the desired value. The polarized caps are to be just under twice the desired value and hooked up back-to-back with a 1MΩ pull-up resistor to a 9V battery (after Infinity, JBL, etc).

The basic idea has a brief mention in one of the early Loudspeaker Design Cookbook, it may be in the newer versions as well.
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Old 10th April 2011, 03:47 AM   #3
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Quote:
Originally Posted by georgehifi View Post
Hi guys no too up on this, has anyone tried it? I cannot find much info on this at all.
I have two ACI SV12 on the bottom (60lt sealed heavy stuffed) of my Martin Logan ESL Monoliths active 24db crossed over at 150hz, they sound very very good compared to the rubbish Eminence drivers ML put in there originally.
I've since been made aware of this (attached) that ACI put out which is a series 2500uf cap with the driver that flattens out and extends the response. I know that it lowers the effiecency by around 2db, but it takes out the slight hump and goes down further.
Is there any disadavtage like damping control over the cone?
I have ordered 4 X Nippon Chemi-con 4700uf caps that back to back will give me 2350uf, but these are standard caps and I believe that very low esr ones should be use, but I cannot find any cheap enough for this experiment.
Any thoughts on this by anyone?

Also I believe that B&W used this on their 801's and Infinity on their IRS and more expensive range, both these manufacturers always seamed to get great bass from their designs?
It also can also can protect the driver from an amp that goes DC

Cheers George
Infinity uses this on some of their models including the RS-2's not on the IRS.

http://www.infinity-forum.de/downloa...ical_sheet.pdf

I believe there was a paper written years ago in the AES on this subject. The author was someone who worked at KLH.
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Old 10th April 2011, 05:29 AM   #4
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Thanks djk for the explanation, made me try it out with some crap old Chinese electro's back to back to get 2350uf that I had in my junk bin.
What I can say is with a familiar big kettle drum track that decays each stroke into the background with good spacing between strokes that I A/B'd it with. With the series cap I can hear/feel it quiver all the way down even at the reduced 2db level. With the cap bridged out it still decays down but the quiver is not felt or heard. So it's a definite plus.
This flys in the face of what I've aways believed in, that capacitor coupling sucks if you can direct couple. For me now the advantages out weigh the disadvantages of capacitor coupling in this case.
djk you think that low esr caps are not needed in this setup? My standard Nippon Chemi-Con that I purchased on ebay will suffice? http://cgi.ebay.com.au/ws/eBayISAPI....=STRK:MEWNX:IT
Thanks George
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Last edited by georgehifi; 10th April 2011 at 05:31 AM.
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Old 10th April 2011, 02:35 PM   #5
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Those should be OK with the bias circuit. The 120hz/100hz ripple current spec is more important then the ESR for this circuit. Try a 10F film bypass too.
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